Methods to obtain varying densities of Ag nanoparticles on YSZ silicon wafer

• Main Author: Ooi, Ching Fei.
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering
• Online Access: http://hdl.handle.net/10356/55111
• Institution: Nanyang Technological University

The objective of this final year project (FYP) is to create masks with varying densities of silica so as to obtain different densities of Ag nanoparticles on yittra-stabilized zirconia (YSZ) silicon wafer. In this project, mono-dispersed silica nanoparticles of about 200 nm in diameter were first fabricated from chemical reaction of tetraethyl orthosilicate (TEOS), ammonium hydroxide and ethanol. A spin coating approach was then used to coat wafers of 2 cm by 2 cm with the fabricated silica, after which the wafer was then deposited with Ag of thickness 100 nm and 500 nm through DC sputtering. To achieve different densities of silica, spin coating parameters such as time taken for acceleration, time taken for deceleration, spin speed and spin time were varied during the experiment. Additionally, poly-acrylic acid was also experimented with by heating a wafer in it at 80°C for 1 hour to reduce the surface tension of the wafer surface to obtain a greater density of silica. In this project, two methods were explored in order to remove the silica mask after Ag was sputtered. One of the methods was using potassium hydroxide to etch away the silica mask. In this method, the wafer was placed in a solution of potassium hydroxide at 60°C. However, this method was later abandoned because it ‘peeled off’ the whole layer of silica mask together with the Ag, instead of just etching away the silica mask. The second method consisted of placing the wafer in deionized water and subjecting it to ultrasonic cleaning. Many masks have been fabricated using the spin coating approach and with various controlled parameters, the masks were then examined under a scanning electron microscope (SEM), it was noted that the main influencing parameters of the spin coating are the spin speed and the spin time. A spin speed of 1000 rpm resulted in a silica mask density of around 48%, while a spin speed of 3000 rpm resulted in a density of around 20%. The application of ultrasonic cleaning machine has been proven effective in removing the silica mask with Ag layer of 100 nm thickness. The project proves that spin coating is a feasible approach in making random masks with uniformly spread Ag nanoparticles. Additionally, ultra sound approach is effective in removing masks from the surface of the silicon wafer.